晶粒尺寸变化不锈钢对抗拉疲劳强度的影响及其断裂机理研究

In the design of component anti-fatigue, fatigue notch factor (Kf) is an important parameter to evaluate fatigue strength on a notch. The quantitative relationship between notch fatigue strength and tensile strength, makes difficulties in studying the notch fatigue strength. When grain size including coarse grain, fine grain, ultra fine grain and nanocrystalline is different, the representation method of fatigue strength and tensile strength is studied in this project, to analyze and forecast the fatigue fracture mechanism of the size effect on austenitic stainless steel. Based on the detailed study of multi-scale and multi-strength microstructure grains, the tensile fatigue strength model of microstructure is established. The quantitative relationship between the notch fatigue strength and tensile strength is calculated. The internal relations among the tensile deformation mechanism, fatigue cracking mechanism, the fatigue strength and grain size parameters is investigated. The theories and methods of the grain size effect on tensile fatigue strength are proposed, in order to explain the grain size effect on notch fatigue strength and reveal the influence mechanism of microstructure, tensile strength on the notch fatigue strength of the system. This project belongs to the basic issues and research frontiers of the interdiscipline, to provide an experimental basis and theoretical guidance for fatigue strength prediction and optimization design. The study has important scientific significance and application value.

在构件抗疲劳设计中，疲劳缺口系数(Kf)是评价缺口处疲劳强度的重要参量，它与拉伸强度的定量关系，是缺口处疲劳强度研究领域的难点。本项目拟研究不同晶粒尺寸下（粗晶、细晶、超细晶到纳米晶），奥氏体不锈钢的拉伸疲劳强度，实现奥氏体不锈钢尺寸效应的拉伸疲劳断裂机理分析与探讨。在深入研究多尺度、多强度级别晶粒微观组织结构的基础上，建立基于微观组织的拉伸疲劳强度模型；理论分析与计算缺口疲劳强度和拉伸强度的定量关系；探讨奥氏体不锈钢拉伸形变机制、疲劳开裂机制与缺口处疲劳强度和晶粒尺寸参数的内在关系，提出缺口处拉伸疲劳强度晶粒尺寸效应分析理论与方法，解释缺口处疲劳强度晶粒尺寸效应问题，揭示微观组织结构、拉伸强度对缺口疲劳强度的影响和规律。该项目属于交叉学科的基础性问题和研究前沿，为疲劳强度预测和材料优化设计提供实验依据与理论指导，具有重要的科学意义和应用价值。

在构件抗疲劳设计中，疲劳缺口系数(Kf)是评价缺口处疲劳强度的重要参量，它与拉伸强度的定量关系，是缺口处疲劳强度研究领域的难点。本项目以具有较好应用前景的等通道转角挤压方法制备微米晶/纳米晶结构304不锈钢，研究变形量和晶粒尺寸对微米晶/纳米晶组织、拉伸疲劳性能、变形和失效机制的影响及作用机制，建立基于微观组织的拉伸疲劳强度模型，揭示奥氏体不锈钢拉伸形变机制、疲劳开裂机制与缺口处疲劳强度和晶粒尺寸参数的内在关系，提出缺口处拉伸疲劳强度晶粒尺寸效应的分析理论与方法。获得拉伸强度大1000MPa、屈服强度大于850MPa，延伸率大于20%和良好腐蚀性能的微米晶/纳米晶结构304不锈钢铸坯设计方法；基于真实应力应变曲线，建立了一种新型疲劳强度预测模型，该模型精度高、成本低。